Membrane-free redox flow battery: From the idea to the market

The increasing global energy demand and the transition toward a more sustainable energy system necessitate the integration of renewable sources, emphasizing the need for effective energy storage systems. Redox flow batteries (RFBs) are particularly suitable due to their efficiency and unique ability to decouple energy and power density. However, their widespread adoption is hindered by the high costs of ion-selective membranes and vanadium-based electrolytes currently used in commercial vanadium RFBs. This study analyzes an alternative membrane-free (membraneless) flow battery technology that relies on immiscible electrolytes, which spontaneously separate into two distinct liquid phases, eliminating the need for an ion-selective membrane or any other kind of physical separator. This approach promises to address key hurdles in advancing RFB technology by reducing overall costs while enhancing sustainability and overall performance. Here, we examine the fundamentals, evolution, and development needed for market implementation of this innovative technology. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/).